With a widespread use of a mobile device, users are increasingly relying on viewing time through the mobile device. However, as a screen of the mobile device is frequently switched on for viewing time, power consumption is relatively high, thereby greatly shortening battery life of the mobile device. In related arts, the mobile device may have an Always-On function to achieve a long-time display without operations on the screen. However, an implementation of the Always-On function still requires waking up an application processor (AP for short) at a certain interval (such as every one minute) to compute device time. As power consumption caused by waking up the application processor to compute the device time is relative high, power of the mobile device may be consumed in a high speed, thereby greatly shorten the battery life of the mobile device.